The bioelectric parameters of the vagina during the oestrous cycle of the rat.

1. A new in vitro preparation of the rat vagina was devised to allow the measurement of the electrical potential difference (p.d.), short-circuit current (s-c.c.) and tissue resistance. 2. In vivo and in vitro, the magnitude of the transvaginal p.d. (adventitia positive to lumen) was greatest at oestrus and smallest at dioestrus and metoestrus. The p.d. at pro-oestrus was not significantly different from the latter values. 3. The s-c.c. was significantly greater at oestrus than at metoestrus, dioestrus and pro-oestrus. 4. The vaginal resistance was maximal at pro-oestrus and was significantly greater than that at metoestrus, dioestrus and oestrus. The value at oestrus was significantly greater than that at metoestrus and dioestrus. These changes in resistance correlate well with known changes in vaginal morphology during the oestrous cycle. 5. It is proposed that the cellular site for the generation of vaginal bioelectric activity is the basal cell layer of the vagina and that the variations of the transvaginal p.d. measured in vivo are caused by the changes in vaginal current and tissue resistance.